<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    html{
        font-size: 10px;
    }

    span{
        /* font-size: 2rem; */
        font-size: 2.8rem;
    }
</style>
<body>
    <!-- 
        rem 相对html的字体大小的变化

        html font-size 16px = 1rem
     -->

    <span>测试</span>
    
</body>
</html>